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本篇将介绍在JNI编程中C调用Java实现。 源码下载地址:[http://download.csdn.net/detail/xyz_lmn/4868265](http://download.csdn.net/detail/xyz_lmn/4868265) 关键代码: **java:** ~~~ public class CCallJava { public static String getTime() { Log.d("CCallJava", "Call From C Java Static Method" +String.valueOf(System.currentTimeMillis())); return String.valueOf(System.currentTimeMillis()); } public void sayHello(String msg) { Log.d("CCallJava", "Call From C Java void Method" +String.valueOf(System.currentTimeMillis())); } } ~~~ **C:** ~~~ #include "TestCCallJava.h" #include <android/log.h> extern JNIEnv* jniEnv; jclass TestCCallJava; jobject mTestCCallJava; jmethodID getTime; jmethodID sayHello; int GetTestCCallJavaInstance(jclass obj_class); /** * 初始化 类、对象、方法 */ int InitTestCCallJava() { __android_log_print(ANDROID_LOG_INFO, "JNIMsg", "InitTestCCallJava Begin 1" ); if(jniEnv == NULL) { return 0; } if(TestCCallJava == NULL) { TestCCallJava = (*jniEnv)->FindClass(jniEnv,"com/trunkbow/ccalljava/CCallJava"); if(TestCCallJava == NULL){ return -1; } __android_log_print(ANDROID_LOG_INFO, "JNIMsg", "InitTestCCallJava Begin 2 ok" ); } if (mTestCCallJava == NULL) { if (GetTestCCallJavaInstance(TestCCallJava) != 1) { (*jniEnv)->DeleteLocalRef(jniEnv, TestCCallJava); return -1; } __android_log_print(ANDROID_LOG_INFO, "JNIMsg", "InitTestCCallJava Begin 3 ok" ); } if (getTime == NULL) { getTime = (*jniEnv)->GetStaticMethodID(jniEnv, TestCCallJava, "getTime","()Ljava/lang/String;"); if (getTime == NULL) { (*jniEnv)->DeleteLocalRef(jniEnv, TestCCallJava); (*jniEnv)->DeleteLocalRef(jniEnv, mTestCCallJava); return -2; } __android_log_print(ANDROID_LOG_INFO, "JNIMsg", "InitTestCCallJava Begin 4 ok" ); } if (sayHello == NULL) { sayHello = (*jniEnv)->GetMethodID(jniEnv, TestCCallJava, "sayHello","(Ljava/lang/String;)V"); if (sayHello == NULL) { (*jniEnv)->DeleteLocalRef(jniEnv, TestCCallJava); (*jniEnv)->DeleteLocalRef(jniEnv, mTestCCallJava); (*jniEnv)->DeleteLocalRef(jniEnv, getTime); return -3; } __android_log_print(ANDROID_LOG_INFO, "JNIMsg", "InitTestCCallJava Begin 5 ok" ); } __android_log_print(ANDROID_LOG_INFO, "JNIMsg", "InitTestCCallJava Begin 6" ); return 1; } int GetTestCCallJavaInstance(jclass obj_class) { if(obj_class == NULL) { return 0; } jmethodID construction_id = (*jniEnv)->GetMethodID(jniEnv, obj_class, "<init>", "()V"); if (construction_id == 0) { return -1; } mTestCCallJava = (*jniEnv)->NewObject(jniEnv, obj_class, construction_id); if (mTestCCallJava == NULL) { return -2; } return 1; } /** * 获取时间 ---- 调用 Java 方法 */ void GetTime() { if(TestCCallJava == NULL || getTime == NULL) { int result = InitTestCCallJava(); if (result != 1) { return; } } jstring jstr = NULL; char* cstr = NULL; __android_log_print(ANDROID_LOG_INFO, "JNIMsg", "GetTime Begin" ); jstr = (*jniEnv)->CallStaticObjectMethod(jniEnv, TestCCallJava, getTime); cstr = (char*) (*jniEnv)->GetStringUTFChars(jniEnv,jstr, 0); __android_log_print(ANDROID_LOG_INFO, "JNIMsg", "Success Get Time from Java , Value = %s",cstr ); __android_log_print(ANDROID_LOG_INFO, "JNIMsg", "GetTime End" ); (*jniEnv)->ReleaseStringUTFChars(jniEnv, jstr, cstr); (*jniEnv)->DeleteLocalRef(jniEnv, jstr); } /** * SayHello ---- 调用 Java 方法 */ void SayHello() { if(TestCCallJava == NULL || mTestCCallJava == NULL || sayHello == NULL) { int result = InitTestCCallJava() ; if(result != 1) { return; } } jstring jstrMSG = NULL; jstrMSG =(*jniEnv)->NewStringUTF(jniEnv, "Hi,I'm From C"); __android_log_print(ANDROID_LOG_INFO, "JNIMsg", "SayHello Begin" ); (*jniEnv)->CallVoidMethod(jniEnv, mTestCCallJava, sayHello,jstrMSG); __android_log_print(ANDROID_LOG_INFO, "JNIMsg", "SayHello End" ); (*jniEnv)->DeleteLocalRef(jniEnv, jstrMSG); } ~~~ 关键代码说明: **C中定义映射的类、方法、对象** ~~~ jclass TestCCallJava; jobject mTestCCallJava; jmethodID getTime; jmethodID sayHello; ~~~ **InitTestCCallJava()方法初始化类、方法、对象** 初始化类: ~~~ TestCCallJava = (*jniEnv)->FindClass(jniEnv,"com/trunkbow/ccalljava/CCallJava"); ~~~ 初始化对象: ~~~ mTestCCallJava = (*jniEnv)->NewObject(jniEnv, obj_class,construction_id); ~~~ 初始化方法: 静态方法: ~~~ getTime = (*jniEnv)->GetStaticMethodID(jniEnv, TestCCallJava, "getTime","()Ljava/lang/String;"); ~~~ 非静态方法: ~~~ sayHello = (*jniEnv)->GetMethodID(jniEnv, TestCCallJava, "sayHello","(Ljava/lang/String;)V"); ~~~ **C 中调用 Java的 方法** 调用静态方法: ~~~ jstring jstr = NULL; char* cstr = NULL; __android_log_print(ANDROID_LOG_INFO, "JNIMsg", "GetTime Begin" ); jstr = (*jniEnv)->CallStaticObjectMethod(jniEnv, TestCCallJava, getTime); cstr = (char*) (*jniEnv)->GetStringUTFChars(jniEnv,jstr, 0); __android_log_print(ANDROID_LOG_INFO, "JNIMsg", "Success Get Time from Java , Value = %s",cstr ); __android_log_print(ANDROID_LOG_INFO, "JNIMsg", "GetTime End" ); ~~~ 调用非静态方法 ~~~ jstring jstrMSG = NULL; jstrMSG =(*jniEnv)->NewStringUTF(jniEnv, "Hi,I'm From C"); __android_log_print(ANDROID_LOG_INFO, "JNIMsg", "SayHello Begin" ); (*jniEnv)->CallVoidMethod(jniEnv, mTestCCallJava, sayHello,jstrMSG); __android_log_print(ANDROID_LOG_INFO, "JNIMsg", "SayHello End" ); ~~~ 注意 GetXXXMethodID  和 CallXXXMethod 。 第一个XXX 表示的是映射方法的类型,如: 静态 跟非静态 第二个 XXX 表示 调用方法的返回值 ,如:Void,Object,等等。(调用静态方法的时候Call后面要加Static) 详细 映射方法 和 调用方法 请参考 [JNI 文档](http://files.cnblogs.com/luxiaofeng54/JNI_Docs.rar) ,这个很重要 ! **工程的其他代码可在[http://download.csdn.net/detail/xyz_lmn/4868265](http://download.csdn.net/detail/xyz_lmn/4868265)下载** **参考:** [http://game.ceeger.com/Script/AndroidJNI/AndroidJNI.html](http://game.ceeger.com/Script/AndroidJNI/AndroidJNI.html)